This invention relates to a safety device for a robot, which maintains an input-output circuit high in reliability which is to externally control a robot body.
In general, an industrial robot in a teaching play-back system employs a teach pendant (TP). The teach pendant (TP) is useful for teaching the robot when the operator finely moves robot body watching a controlled point (end effector) of the industrial robot.
The teach pendant (TP) has an emergency stop switch to secure the operator from danger. The emergency stop switch is electrically series-connected to an emergency stop circuit. Therefore, when the switch is operated, a servo power supply for driving a robot body is turned off.
The servo power supply for driving a robot body is provided with safety circuits such as a door stop detection circuit and an external emergency stop circuit, so that the servo power supply is turned off when a door stop input or an external emergency stop input is applied.
When the robot operator operates the emergency stop switch of the teach pendant (TP), or when he operates the door stop input circuit or the external emergency stop circuit in the safety circuit, the servo power supply for driving a motor of an industrial robot is turned off, and the lock (brake) of the shaft of the servo motor is operated.
Now, a conventional industrial robot safety device will be described with reference to FIG. 4.
If, when a panel/external service "on" switch 110 is closed, there is no factor (the emergency stop circuit input signal such as the door stop input signal, the external emergency stop signal) which interrupts the application of servo power to the robot body, then a CPU (not shown) fixes a CPU servo power supply ON output signal at HIGH logic level with the aid of a flip-flop circuit (not shown). In this case, relay coils CR18, CR14, CR17, and CR16 have been excited; that is, their relay contact means CR18a, CR14a, CR17a and CR16a have been closed. Hence, a voltage (+24VDC in the case of FIG. 4) is induced on a servo application permission signal line 12, so that the servo power application circuit is driven.
As shown in FIG. 2, the robot body 1 is set in a safety cage 2 at all times, and the safety fence has a door 5 through which the operator goes in and out of the cage. When the door 5 is opened, a door stop input switch 105 is operated. When the switch contact means is opened, of the door stop input signal is interrupted, and a contact means 105b is opened which are connected to the door stop input line 105a and a circuit ground (PG). Therefore, the CPU recognizes the door stop input signal operation with the aid of a photo-coupler group 22, while the relay CR16 is deexcited, and the contact means CR16a is opened, so that the servo supply is turned off.
As is apparent from the above description, the door stop input switch 105 and other emergency stop circuits (a TP emergency stop input switch 104, an external stop input switch 103, and a panel emergency stop input switch 107) excite the relay coils CR16, CR14, CR17 and CR18 of the emergency stop circuits, thereby to series-connect their relay contact means to the servo application permission signal line 12 as shown in FIG. 4. Therefore, if any one of the external input signals (no voltage switch) of the safety circuits is turned off, the servo application permission signal line 12 is interrupted, thereby to turn off the servo supply.
In the case where the various emergency stop circuits operate to interrupt the servo application permission signal line 12 of the robot body 1, or the CPU in the robot control device 3 recognizes the aforementioned operations or other abnormal states, the CPU emergency stop output signal 11 is fixed at LOW logical level with the aid of a flip-flop circuit (not shown). Therefore, in this case, the relay CR1 is deexcited, so that the relay contact means CR1a is opened to inform external equipments of the emergency stop state.
When the work preparation of the robot body 1 has been accomplished, the robot control device 3 applies a general purpose output n 106a to an external control board 6. In response to the general purpose output n 106a, the external control board 6 operates a workpiece supply device 8 to supply a workpiece into the operating range of the robot body 1. Upon completion of the supply of a workpiece, the external control board 6 causes a general purpose input 106g to short-circuit with a circuit ground 106h thereby to apply a signal to the robot control device 3. In response to the input signal, the robot control device 3 starts control to cause the robot body 1 to perform a predetermined operation (work). As is apparent from the above description, the robot body 1 and the workpiece supply device cooperate with each other to perform a series of work. For this purpose, the robot control device 3 are provided with general purpose input n (n being natural numbers) and general purpose output n (n being natural numbers) to transmit signals between itself 3 and the external control board 6.
As was described above, in the conventional industrial robot safety device, the servo power supply circuit of the robot is interrupted by using the limit switch or the relay contact means--for instance by operating the emergency stop input switch 104 of the teach pendant (TP) 4 to open the switch contact means. In order to turn on or off the servo power supply, the switch or the relay contact means is operated. Therefore, if the driven line (105a, 103a, 104a, 107a, 110a, 106g, or 106b) in the group 21 of wires is grounded which is connected between the switch and the input and output sections in the robot control device 3, the variety of emergency stop signals, and the operation of the general purpose input signal n, or the general purpose output signal n is not correctly transmitted, so that the predetermined functions are not correctly performed.
Furthermore, in the case where the relay contact means CR1a indicating the emergency stop output is fused, the input and output signals are not correctly transmitted. In addition, since the contact means should function as a no-voltage contact means, it is impossible for the side of the robot control device 3 to detect that the contact means has been fused.